The sexual agglutination system of Saccharomyces cerevisiae is a specific cell-cell adhesion system that is amenable to biochemical and molecular biological analysis. We have isolated the glycoprotein alpha-agglutinin and in collaboration of Dr. Janet Kurjan, identified, cloned, and sequenced its structural gene, AGalpha1. We intend to continue the collaboration to investigate the structure of alpha-agglutinin. The alpha-agglutinin sequence will be dissected to identify a cell binding and cell wall anchorage domains. We will then further define these domains by in vitro mutagenesis and assays of expression for both binding and anchorage. Since alpha-agglutinin is the only yeast cell wall protein of known sequence and function, we can use this information to probe cell wall architecture and the mechanism of cell wall biosynthesis Additionally, we will determine whether alpha-agglutinin is synthesized with a phosphoinositide glycan intermediate. We will also clone and sequence the genes for the complementary glycoprotein a-agglutinin. Putative a-agglutinin mutants have been isolated and complemented with DNA fragments from a yeast clone bank. The cloned genes will be used to try to identify sequences necessary for alpha-agglutinin binding in the weak and tight modes, and to assess the relative physiological importance of the two modes.